The present invention relates generally to the production of reinforcing fabric, and more particularly to an improved apparatus for formation of non-woven net fabrics used as reinforcement for composite material which is composed of thermosetting resin reinforced by reinforcing fiber having high strength, rigidity and modulus, for example graphite fiber, aromatic polyamide fiber and the like.
The present inventors have previously proposed, as shown in FIG. 1, an invention relating to a reinforcing non-woven fabric suitable for use as reinforcement for composite material in Japanese patent applicaton Tokugansho No. 56-203870 (corresponding to U.S. patent application Ser. No. 449800 and EPC applicaton Ser. No. 82111583.9.)
According to the above invention, the non-woven fabric has three-layer structure comprising upper and lower warp sheets WA-I and WA-II, and a weft sheet WE sandwiched between the pair of warp sheets, and is formed by a method comprising a step of impregnating adhesive into the weft thread of the weft sheet WE and a step of respectively supplying the pair of warp sheets WA-I and WA-II to both sides of the weft sheet WE with no adhesive thereon and simultaneously pressing and bonding the sheets to each other at their intersection points to form a composite sheet of warp and weft sheets, i.e. a non-woven fabric. Accordingly, the adhesive is impregnated only in the weft threads and is present at the intersection points of the warp threads. Thus, when using said non-woven fabric as reinforcement for the resinous composites, the resin can readily and sufficiently permeate especially into the warp threads, resulting in a resinous composite having high strength.
In U.S. Pat. No. 3,728,195 there is disclosed an apparatus for production of reinforcing non-woven net fabrics in which a pair of warp sheets, and a weft sheet to be sandwiched between the warp sheets are initially brought together in co-planar relationship, and these sheets are subsequently dipped in an adhesive bath, and finally these sheets are dried so as to be bonded to each other.
The non-woven fabric formed by the conventional apparatus as described above, however, has some drawbacks. For instance, when using it as reinforcement for the resinous composites, the resin can not sufficiently permeate into either the warp or the weft threads since the adhesive has been previously coated on most of the peripheral surfaces of the threads, and thus sufficient reinforcing effect by the non-woven net fabric is not available. In addition, during passing of the composite of the warp and weft sheets through the adhesive bath, misplacement of the threads occurs. These threads should be arranged in parallel and equally spaced relationship in order to obtain high strength.